Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, medical devices, automobiles, portable electronic devices and other applications. The technology used to manufacture image sensors, and in particular CMOS image sensor (“CIS”), has continued to advance at a great pace. Modern image sensor applications place demands for faster processing speeds and better image quality, while simultaneously expecting miniaturization in the physical size of the image sensor.
As the physical size of the image sensor gets smaller the need to use smaller MOS transistors increases. However, the use of small MOS transistors in image sensors brings with it various noise sources, such as white (Johnson) noise, 1/f noise, and random telegraph signal (RTS) noise. Conventional image sensors may be designed and fabricated using advanced CMOS process techniques and with advanced transistor devices, such as buried channel transistors, in an attempt to minimize noise, such as RTS noise. However, often even when implementing these techniques some noise, such as RTS noise, may remain.